It is frequently desirable but inherently difficult to move substantial amounts of solid particles in a controllable way through systems of vessels and conduits. A major obstacle to such control is that conventional valves which are the method of choice for controlling the transport of fluids are subject to undue amounts of abrasion and wear and tear when operated in the presence of solid particles. Nevertheless, a number of industrial scale processes require the use of solids, such as water treatment, separations and purifications employing ion exchange resins, and, perhaps most prominently, processes which are conducted under the influence of a solid catalyst.
The petroleum industry has for many years been a major user of such processes and, in this instance, the problem is further aggravated by the necessity for maintaining high temperature and pressure conditions in reaction vessels as well. In a large number of petroleum refining processes, such as reforming, and such hydroprocessing reactions as demetalization and desulfurization, fluid feedstocks are reacted in the presence of substantial amounts of solid particulate catalytic materials, which catalytic materials are subject to deactivation during the reactions they facilitate. Accordingly, typically a particular sample of catalyst becomes spent in a relatively short period of several weeks to a few months. It is, then, clear that the transfer of solid particles becomes necessary for at least two reasons--first, for sampling purposes to ascertain whether or not replacement is necessary and, second, movement of large amounts of catalyst into and out of reactors to secure a fresh supply of catalyst. Of course, the latter problem can be solved by dismantling the reactor when the catalyst is sufficiently spent; and the former can be obviated by a precalibrated system of continuous catalyst replacement. However, in either case, it is necessary to move the solid catalyst particles in a controlled way from the inside of the reaction vessel to an accessible position outside of it.
The problem of removing small sample amounts of catalyst from the reaction vessel for assessment purposes has been approached in a number of ways. U.S. Pat. No. 3,561,274 to Haunschild discloses a sampler for use in densely packed reaction vessels operating at high pressure which takes advantage of a mechanical rotating action to dislodge samples of solids, which are encouraged to exit the vessel by a combination, apparently, of gravity and pressure differential. The flow can be shut off either by mechanical valving, or by the natural resistance of the particles to flow.
U.S. Pat. No. 3,973,440 discloses a device which encourages initial upward vertical flow followed by a gravity-assisted drop. It is suitable to a densely packed bed of solid particles. This device draws material into the outlet tube by a sudden decrease in pressure following clearing the sampling tube with a heated purge gas. During operation, the flow of solids is controlled in part by valves in the exit line.
U.S. Pat. No. 3,487,695 also to Haunschild uses an external supply of gas to clear a vertical gravity assisted path for removal of a small sample of solid particles from a densely packed reactor. The removal path is an uninterrupted downward flow.
U.S. Pat. No. 3,653,265 uses the differential pressure between the reaction vessel and a solids receiver to create a gas stream wherein the catalyst flow is driven upward and out. The flow is controlled by an offsetting quantity of purge gas.
U.S. Pat. No. 3,336,217 to Meaux takes advantage of an ebullant bed situation in a reactor vessel to fluidize the particulates in such a way that, unless counterpressure is applied, the particles are capable of traveling up and out of the vessel past a valve. To terminate the flow of particles, the mechanical valve in their path is closed and the sampling tube purged with a gas stream.
The foregoing procedures appear suitable for withdrawal for small portions of catalyst for sampling purposes. Those withdrawal ports which operate on dense-packed solids agitate small quantities desirable for sampling. Where a densely-packed bed is not available to offer resistance to flow, as in U.S. Pat. No. 3,336,217, the withdrawal tube relies on mechanical valves in the port to stop the flow of particles. Those systems which are designed for packed beds rely on purge gas systems to create clear pathways for particulate transport.
Other approaches have been taken where movement of catalyst is required as an integral part of the process which is carried out as a catalyzed reaction in a high temperature and pressure reaction vessel. A number of such processes related to hydroprocessing which include catalyst exchange have been proposed. For example, U.S. Pat. No. 3,826,737 discloses a continuous process for catalytic treatment of hydrocarbons where the catalyst flows cocurrently with the process stream downward through the reactor and is withdrawn through a system of valves from the bottom of the vessel. U.S. Pat. No. 3,880,598 discloses both a cocurrent and countercurrent process again withdrawing solids directly from the bottom of the reactor. U.S. Pat. No. 4,259,294 proposes a series of cocurrently moving bed reactors supplied from a single catalyst reservoir, but again, catalyst is withdrawn directly from the bottom of the vessels. A number of other cocurrent and countercurrent processing systems, wherein catalyst is moved through the reactor on either a continuous or a controlled intermittent basis are disclosed in U.S. Pat. Nos. 3,910,834, 3,795,607, 4,312,741, and 3,716,478. In all of the foregoing, the catalyst is simply withdrawn from the bottom of the reactor and, thus, the flow, to the extent that it is controlled, must be regulated at least to some extent by mechanical valving sytems.
An alternate system, disclosed in U.S. Pat. No. 3,716,478, relies on a liquid discharge from an opposing tube whose inlet port is positioned directly opposite the incoming fluid conduit. The exit conduit is placed in a horizontal position but mechanical valves remain in the system.
For gas/solid systems only, such as those employed in petroleum reforming, it has been disclosed that an inverted U-tube catalyst withdrawal system which relies on periodic release of a gas-flow created counter pressure in the inverted U can be used (copending application Ser. No. 537,023, filed Sept. 29, 1983, and assigned to the same assignee).
The present invention offers a catalyst withdrawal and dumping system which is adaptable to large-scale liquid medium based hydroprocessing reactions in high-pressure vessels. It utilizes a fluid-controlled valving system wherein the fluid contacting these particles is liquid to move particles from a densely packed catalyst bed to a receiving vessel external to the reaction chamber. The apparatus and method of the present invention can be used, of course, for sampling purposes as well. While mechanical valves can be included in the system within the path of transport of the solid particles, their use is not an inherent part of the system, and the flow of catalyst particles can be controlled entirely by pressure regulation in parts of the system which do not experience direct particle flow.